Electromagnetic interference detection system for mass transit vehicles with electronic propulsion

ABSTRACT

An electric power vehicle includes a propulsion system connected to a direct current (DC) source via a supply line. The propulsion system converts the DC supplied via the supply line to an AC electrical power to operate an AC motor at a desired level. An electromagnetic interference detection system for the vehicle includes an EMI processor connected to a current transducer and the propulsion system. The transducer detects AC signals appearing on the supply line and provides an output to the EMI processor. The EMI processor determines the frequency, amplitude and duration of the detected AC signals and causes the propulsion system to adjust the AC electrical power supplied to the motor as a function thereof.

BACKGROUND OF THE INVENTION

This application is a 371 of PCT/US96/10279 filed Jun. 13, 1996, whichis a continuation of Provisional Application Ser. No. 60/000,219 filedJun. 13, 1995.

1. Field of the Invention

The present invention relates to mass transit vehicles powered fromexternal sources of electrical power and, more particularly, to systemsfor detecting electromagnetic interference during the operation of masstransit vehicles.

2. Background Art

An electrically powered mass transit vehicle typically includes apropulsion system connected to a direct current (DC) motor oralternating current (AC) motor for propelling the vehicle on runningrails. The propulsion system is often driven by a source of DCelectrical power supplied from a remote source via a supply line, suchas a power rail or an overhead power line. The DC power is oftensupplied at a relatively high voltage to minimize power loss associatedwith resistive drops along the length of the supply line. A return pathfor the DC electric power is provided via the running rails. It is to beappreciated that the DC electrical power, and more specifically, the DCcurrent, provided to the vehicle via the supply line also flows in therunning rails. It is common to use the running rails to also provide ACcontrol signals to track signaling equipment, e.g., wayside aspectlights, associated with the rail or track system. These AC controlsignals are provided at predetermined frequencies, e.g., 60 Hz and 100Hz. To provide for operation of the track signaling equipment duringoperation of the vehicle, these AC control signals are superimposed onDC current in the running rails.

The electric motor of a mass transit vehicle is typically designed forvariable speed operation at voltages and currents other than provided bythe supply line. To accomplish variable speed operation, it is common toswitchably control the power supplied to the motor. To this end, forvehicles equipped with a DC motor, the propulsion system includes aDC-DC converter for converting supplied DC to a DC useable by the motor.Similarly, for vehicles equipped with an AC motor, the propulsion systemincludes a DC-AC inverter for changing the supplied DC to an AC useableby the motor. In operation, the DC-DC converter or the DC-AC invertercontrollably switches power from the supply line to the motor as afunction of the desired operating characteristics thereof. Specifically,less power is switched from the supply line to the motor when lowervehicle speeds or motor torque are desired and more power is switchedfrom the supply line when higher vehicle speeds or motor torque aredesired. A characteristic of the operation of the DC-DC converter or theDC-AC inverter is that AC electrical noise is often conducted onto theDC current. This conducted noise is often generally referred to asElectromagnetic Interference (EMI). Importantly, EMI may containfrequency components in the range of the AC control signals for thetrack signaling equipment associated with the vehicle. Accordingly,there are concerns that such EMI may cause unintended operation of orundesirable interference with the track signaling equipment.

To reduce the effect of EMI on the DC current, standard propulsionsystems include line filters for absorbing significant line currentfrequencies produced by the DC-DC converter or the DC-AC inverter and,more specifically, for absorbing line current frequencies in the rangeof control signals for the track signaling equipment, i.e., 60 Hz and100 Hz. In this manner, the effect of EMI on the DC current by theoperation of the DC-DC converter or DC-AC inverter is reduced.

Line filters are typically designed to provide filtration of noisewithin certain established levels, e.g., without limitation, amplitude,duration and/or frequency. As a result, noise outside the establishedlevels will not be adequately filtered and will be conducted on thesupply line. Moreover, if electrical components, e.g., capacitors,associated with the line filter fail or change value with age, theeffective filtration characteristics of the line filter are changed andnoise normally filtered thereby appears on the DC current. As discussedabove, this is a particular problem where the unfiltered noise hasfrequency components in common with the track signaling equipment, i.e.,60 Hz and 100 Hz.

It is an object of the present invention to provide a system fordetecting undesirable levels of EMI generated by a propulsion system ofan electrically powered vehicle, particularly EMI having frequenciescorresponding to the frequencies of track control signals, and forinitiating corrective action corresponding to the characteristics of thedetected EMI.

SUMMARY OF THE INVENTION

Accordingly, we have invented a method of electromagnetic detection andcontrol in an electrically powered vehicle and an electromagneticdetection and control apparatus. In the method, direct current (DC)electrical power supplied to the vehicle via a supply line is convertedto a power output at a first level and provided to an electric motor.The supply line is monitored for an alternating current (AC) signalappearing thereon. The amplitude and/or duration of the AC signal isdetermined and the power output is adjusted as a function of theamplitude and/or duration of the AC signal.

In accordance with our invention, adjusting the power output includes:maintaining the power output to the electric motor at the first level inresponse to the AC signal being less than a first amplitude for a firstinterval of time; reducing the power output to the electric motor fromthe first level to a second level if the AC signal has an amplitudegreater than the first amplitude for the first interval of time; andwithholding electrical power from the motor if the AC signal has anamplitude greater than a second amplitude, greater than the firstamplitude, for the first interval of time. If the AC signal has anamplitude greater than the second amplitude for a second interval oftime, greater than the first interval, the vehicle is isolated from thesupply line. The isolation of the vehicle from the supply lineterminates the conversion of electrical power and the providing thereofto the electric motor.

The method further includes stimulating a current transducer with analternating current. The stimulating current causes the transducer toproduce an output signal which is detected. At least one of thefrequency, amplitude and duration of the output signal is determined andpower output is provided to the electric motor as a function of the atleast one of the frequency, amplitude and duration of the output signal.

The electromagnetic detection and control apparatus includes a means forconverting electrical power supplied to the vehicle via a supply line toa selectable power output and a means for providing the power output toan electric motor in the vehicle. A means is provided for monitoring thesupply line for an alternating current (AC) signal appearing thereon andfor determining one of an amplitude and duration thereof. The apparatusalso includes a means for adjusting the power output as a function of atleast one of the amplitude and duration of the AC signal.

The apparatus also includes a means for maintaining the power output tothe electric motor at a first level in response to the AC signal beingless than a first amplitude for a first interval of time; a means forreducing the power output to the electric motor from the first level toa second level in response to the AC signal being greater than the firstamplitude for the first interval of time; and a means for withholdingthe power output from the electric motor in response to the AC signalbeing greater than a second amplitude for the first interval of time,wherein the second amplitude is greater than the first amplitude. Theapparatus further includes a means for isolating the vehicle from thesupply line in response to the AC signal being greater than the secondamplitude for a second interval of time, wherein the second interval isgreater than the first interval.

The apparatus includes means for stimulating a current transducer withan alternating current and a means for detecting an output signal of thetransducer in response to the stimulation. A means is provided fordetermining at least one of a frequency, amplitude and duration of theoutput signal and for enabling the providing means to provide poweroutput to the electric motor as a function of the at least one of thefrequency, amplitude and duration of the output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an electrically powered mass transit vehicle inaccordance with the prior art;

FIG. 2 is a block diagram of an electromagnetic interference detectionsystem of the present invention connected to various systems andsubsystems of the vehicle shown in FIG. 1; and

FIG. 3 is a block diagram of the EMI processor shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a prior art electrically powered mass transitvehicle 2 includes a forward disposed alternating current (AC) electricmotor 4A and rearward disposed AC motor 4B for providing motive force tofront and rear wheels 6A and 6B, respectively, so as to propel vehicle 2along a running rail 8. It is to be appreciated that the vehicle 2 hasfront and rear wheels (not shown) disposed on an opposite side thereofand in contact with another rail. The other wheels can have dedicated ACmotors for providing motive force thereto or may be powered from ACmotors 4A and 4B. For convenience, reference will be made hereinafter toAC motors 4A and 4B providing motive force to wheels 6A and 6B. Apantograph 10 conducts direct current (DC) electric power from a supplyline 12 to the vehicle 2. DC electric power conducted by pantograph 10is converted to AC power, by apparatus to be hereinafter described,provided to AC motors 4A and 4B and returned to ground through contactwith the running rail 8. The AC motors 4A and 4B convert the AC powerprovided thereto to motive force of sufficient extent to propel vehicle2 along rail 8. The vehicle 2 could alternatively be equipped with DCmotors.

With reference to FIG. 2 and continuing reference to FIG. 1, vehicle 2includes "A" and "B" propulsion systems 14A and 14B having theirrespective inputs connected to pantograph 10. The outputs of thepropulsion systems 14A and 14B are connected to respective AC motors 4Aand 4B. The propulsion systems 14A and 14B convert DC electric powersupplied thereto to AC electric power useable by AC motors 4A and 4B.For sake of brevity, the propulsion systems 14A and 14B are shown asbeing connected to respective AC motors 4A and 4B. However, it is to beunderstood that propulsion systems 14A and 14B are also connected to ACmotors associated with the respective front and rear wheels on theopposite side of vehicle 2 for providing power thereto. Thus, in theensuing description, reference to propulsion system 14A powering ACmotor 4A is to be understood as also providing power, in parallel, tothe motor associated with the other front wheel. Similar comments applyin respect of propulsion system 14B and the motors associated with therear wheels of vehicle 2. Vehicle 2 also includes an auxiliary powersupply 16 having an input connected to pantograph 10 and an outputconnected to vehicle subsystems 18, such as air conditioners, fans,lights and the like. The auxiliary power supply 16 converts supplied DCelectric power to AC power useable by the vehicle subsystems 18. Thepropulsion systems 14A and 14B and the auxiliary power supply 16 aregrounded to rail 8.

In operation, propulsion systems 14A and 14B controllably switch powerfrom supply line 12 to AC motors 4A and 4B at a level suitable to propelthe vehicle 2 at a selectable rate. In the event one of the propulsionsystems 14A and 14B is inoperative, however, the vehicle is operablefrom the remaining propulsion system, albeit at a reduced vehicleperformance.

Track signaling equipment is often utilized in conjunction with thevehicle 2 to provide suitable warning and control signals concomitantwith the operation thereof. This signaling equipment obtains controlsignals for the selective operation thereof from the running rails 8.These control signals often take the form of alternating current (AC)signals superimposed on the DC current in the running rails 8 atpredetermined amplitudes and frequencies, such as, without limitation,60 Hz, 100 Hz and audio frequencies, for predetermined intervals. It iswell known that the propulsion systems 14A and 14B, switching relativelysignificant power levels at variable frequencies, produce significant ACnoise on the DC current. This AC noise is commonly referred to asElectromagnetic Interference (EMI). Moreover, the auxiliary power supply16 switching lower power levels at a constant operating frequency alsoproduces EMI on the DC current, albeit to a lesser extent than thepropulsion systems 14A and 14B. This EMI often contains components withamplitudes, frequencies and durations in common with the control signalsfor the track signaling equipment. Because such EMI could potentiallyinterfere with the operation of track signaling equipment, prior artpropulsion systems are equipped with input filters, typically aninductor-capacitor circuit, for filtering EMI appearing on the DCcurrent. It is to be appreciated that the input filters may include morethan one inductor and more than one capacitor to achieve a desired levelof filtration.

The system of the present invention, as shown in FIG. 2, includes afilter verification circuit 20A and 20B connected to a respectivepropulsion system 14A and 14B for verifying that the capacitor(s) of theinput filter in an associated propulsion system will provide a desiredlevel of filtration. In operation, each filter verification circuitmeasures the time needed to selectively charge and/or discharge thecapacitor(s) of the corresponding input filter between desired voltagelevels during, for example, a period of vehicle inactivity. Utilizingthe measured charging and/or discharging time, the filter verificationcircuit calculates if the filter capacitance value is within acceptablelimits for filtering EMI below an acceptable noise limit for the outputpower to be provided by the associated propulsion system. If the filtercapacitance value is calculated to be below certain predeterminedacceptable limits, the output of the propulsion system is reduced to alevel wherein EMI produced thereby is normally below the acceptable EMInoise limit for the actual filter capacitance. If additional capacitorsof the input filter fail or change value with age, the output of thepropulsion system is reduced accordingly. If the filter verificationcircuit determines that the actual filter capacitance is below apredetermined lower limit, the filter verification circuit shuts downthe associated propulsion system. The filter verification circuit alsoverifies integrity of one or more fuses associated with one or morecapacitors or capacitor banks of the input filter. If the filterverification circuit determines that one or more fuses are open, thefilter verification circuit selectively reduces or adjusts the poweroutput of the associated propulsion system so that the output of thepropulsion system is reduced to a level wherein EMI produced thereby isnormally below the acceptable EMI noise limit for the available filtercapacitance. In this manner, the output of the propulsion system isadjusted so that EMI produced thereby will normally be below a limitthat could potentially interfere with the operation of track signalingequipment.

The input filter in each propulsion system is designed to provideadequate filtration so that typical levels of EMI produced by thepropulsion system do not interfere with the operation of track signalingequipment. Moreover, each filter verification circuit (20A and 20B) isdesigned to reduce the output of the associated propulsion system as afunction of the available filter capacitance. However, the propulsionsystems may, under abnormal conditions, produce atypical levels of EMIthat would not be adequately filtered by the available filtercapacitance to avoid interfering with the operation of the tracksignaling system. Moreover, partial or complete failure of an inputfilter during operation of the vehicle could produce EMI which would notbe adequately filtered.

Therefore, the present invention includes an EMI detector 24 fordetecting EMI exceeding a selected amplitude for a selected duration andfor adjusting the output of the propulsion system as a function of thedetected EMI. The EMI detector 24 includes a current transducer 26 andan EMI processor 28, which is preferably microprocessor based andsoftware driven. The current transducer 26, such as, without limitation,a transformer, has a means 30 disposed on the vehicle side of pantograph10 for detecting AC signals, and more specifically EMI, appearing on theDC current. The means for detecting AC signals 30 has an outputconnected to an input of the EMI processor 28 for providing scaledrepresentations of the detected EMI signals thereto. The EMI processor28 monitors the scaled signals and measures one or more of theamplitude, frequency and duration of the AC signals on the supply line12. The EMI processor 28 can measure one or more selected frequencies ora frequency spectrum utilizing, without limitation, Fast FourierTransform (FFT), a digital filter or other similar techniques. In apreferred embodiment, if the amplitude of the scaled signals have anamplitude less than or equal to a first amplitude at a selectedfrequency, the EMI processor 28 outputs a condition 0 signal to thepropulsion systems 14A and 14B which interpret the same as an indicationthat the detected EMI is within acceptable limits. Similarly, the EMIprocessor 28 outputs a condition 0 signal to the propulsion systems 14Aand 14B if the scaled signals have an amplitude in excess of the firstamplitude at the selected frequency, wherein said amplitude has aduration less than or equal to a first interval of time. In response toreceiving the condition 0 signal, the propulsion systems 14A and 14Bmaintain output power to the motors 4A and 4B at a first level. It is tobe appreciated that the first level could be established by an operatorof the vehicle 2 or, in an attendantless, automated vehicle, by anintelligent vehicle controller.

If, however, the current transducer 26 detects scaled signals having anamplitude above the first amplitude at the selected frequency, and thefirst amplitude has a duration in excess of the first interval of time,the EMI processor 28 outputs a condition 1 signal to the propulsionsystems 14A and 14B. Moreover, the EMI processor 28 outputs an "ExcessEMI Detected" signal to an EMI Detector Annunciator 32. In response toreceiving the condition 1 signal, the propulsion systems 14A and 14Breduce the power output to the motors 4A and 4B to a second level thatis, for example, 50% of the first level. In response to receiving theExcess EMI Detected signal, the EMI Detector Annunciator 32 provides anaudio or visual indication that excessive EMI has been detected. In apreferred embodiment, the AC signals corresponding to the condition 1signal event do not cause interference with the signaling equipment. Inthis respect, the condition 1 signal event is selected to avoid havingthe AC signals increase in amplitude and/or duration to where acondition 2 or 3 signal, described hereinafter, is generated.

Reducing the power output of the propulsion systems 14A and 14Btypically reduces the amount of EMI generated thereby. Moreover,restoring the power output of the propulsion systems 14A and 14B after abrief interval of reduced power output often results in EMI levels beingwithin acceptable levels. In a preferred embodiment, the EMI processor28 automatically recovers, and outputs a condition 0 signal to thepropulsion system, in response to detecting, for a predeterminedinterval of time, scaled signals having at least one of an amplitude,frequency and duration not corresponding to the EMI processor 28generating a condition 1 signal. Thus, for example, if EMI is, for atleast 5 seconds, below an amplitude corresponding to a condition 1signal event, the EMI processor outputs a condition 0 signal to thepropulsion systems 14A and 14B. In response to receiving the condition 0signal, the propulsion systems 14A and 14B restore the output power tothe first level. If restoring the power output to the first levelproduces EMI levels corresponding to the condition 1 signal event, theEMI processor 28 again outputs a condition 1 signal to the propulsionsystems 14A and 14B. The outputting of a condition 1 signal for apredetermined interval followed by condition 0 signal continues untilthe EMI is within acceptable limits. In this manner, the output of thepropulsion systems 14A and 14B are adjusted for temporal occurrences ofEMI.

In one embodiment, the frequencies, amplitudes and durations of EMIcorresponding to the EMI processor outputting a condition 1 signal are:60 Hz, I>2.8 amps, t>1.0 second; and 100 Hz, I>0.75 amps, t>1.0 second.The frequencies, amplitudes and durations to be detected by the EMIprocessor 28 for generating a condition 1 signal, as well as forgenerating conditions 2 and 3 signals, discussed below, are selected toallow for proper operation of the signaling equipment withoutinterference by EMI generated by the propulsion systems. Similarly, thereduction of output power to 50% of desired output power is intended toreduce EMI noise to an acceptable level but other levels, or even morethan one such level, of power reduction could be used.

If current transducer 26 provides scaled signals having an amplitude inexcess of a second amplitude, greater than the first amplitude, at theselected frequency, and the second amplitude has a duration in excess ofthe first interval of time, the EMI processor outputs a condition 2signal to the propulsion systems 14A and 14B and outputs the Excess EMIDetected signal to the EMI Detector Annunciator 32. In response toreceiving the condition 2 signal, the propulsion systems 14A and 14Bwithhold power from motors 4A and 4B, i.e., the output power is reducedto 0%. In one embodiment, the frequencies, amplitudes and durations ofEMI corresponding to the EMI processor 28 outputting a condition 2signal are: 60 Hz, I>3.7 amps, t>1.0 second; and 100 Hz, I>1.0 amp,t>1.0 second.

In a preferred embodiment, operator intervention is required to recoverfrom a condition 2 signal shutdown of the propulsion systems 14A and14B. Specifically, a resetting means (not shown) provides the EMIprocessor 28 and propulsion systems 14A and 14B with a Propulsion ResetTrainline signal (shown in FIG. 2 as "RESET T/L") in response to anoperator requested reset of the propulsion systems 14A and 14B in thepresence of a brake request at zero vehicle speed. The operator mayrequest up to three operator resets in this manner, whereafter, thepropulsion systems 14A and 14B may only be reset by asserting asupervisory reset (not shown).

In response to receiving the condition 2 signal, the propulsion systems14A and 14B provide the EMI processor 28 with "Level 2 Acknowledge"signals. In the absence of receiving either one or both of the Level 2Acknowledge signals, the EMI processor 28 outputs a condition 3 signalto the propulsion systems 14A and 14B and outputs a "HSCB Trip" signalto a High Speed Circuit Breaker (HSCB) 34. The HSCB 34 is electricallydisposed on the vehicle side of pantograph 10 so that DC electricalpower provided to the vehicle 2 from the supply line 12 passestherethrough. In response to receiving the HSCB Trip signal, the HSCB 34opens and electrically isolates the vehicle 2, and more specifically,the propulsion systems 14A and 14B and the auxiliary power supply 16,from the supply line 12. In this manner, the EMI processor 28 ensuresthat the propulsion systems 14A and 14B and the auxiliary power supply16 are eliminated as sources of EMI noise on the supply line 12.

In the present invention, certain EMI levels are regarded as being ofsufficient extent to merit immediate electrical isolation of the vehicle2 from the supply line 12. To this end, if the current transducer 26provides scaled signals having an amplitude in excess of the secondamplitude at the selected frequency, and the second amplitude has aduration in excess of a second interval of time, greater than the firstinterval of time, the EMI processor 28 outputs the condition 3 signal tothe propulsion systems 14A and 14B and outputs the HSCB Trip signal tothe HSCB 34. Moreover, the EMI processor 28 outputs the Excess EMIDetected signal to the EMI Detector Annunciator 32. As above, the HSCB34 opens in response to the HSCB Trip signal, thereby electricallyisolating the vehicle 2 from the supply line 12.

The EMI processor 28 outputs a condition 3 signal and an HSCB Tripsignal under two circumstances: firstly, if one or both Level 2Acknowledge signals are not received by the EMI processor 28 in responseto outputting a condition 2 signal; and secondly, if scaled signals aredetected corresponding to excessive EMI. In one embodiment, theamplitudes, durations and frequencies of EMI corresponding to EMIprocessor 28 outputting a condition 3 signal under the secondcircumstance are: 60 Hz, I>3.7 amps, t>1.5 seconds; and 100 Hz, I>1.0amp, t>1.5 seconds.

Operator intervention is required to reset the HSCB 34 and thepropulsion systems 14A and 14B after receiving the respective HSCB Tripsignal and the condition 3 signal. In response to an operator requestedreset in the presence of a brake request at zero vehicle speed, theresetting means (not shown) provides the EMI processor 28 and propulsionsystems 14A and 14B with the Propulsion Reset Trainline signal. Inresponse to receiving the Propulsion Reset Trainline signal, propulsionsystems 14A and 14B and the HSCB 34 reset. The operator may request upto three resets in this manner, whereafter, the propulsion systems 14Aand 14B and the HSCB 34 may be reset only by asserting a supervisoryreset.

With reference to FIG. 3 and continuing reference to FIG. 2, the EMIprocessor 28 includes a software driven digital signal processor (DSP)36, an analog data acquisition interface 38, a self test circuit 40, amemory system such as an EPROM 42, an input buffer 44 and an outputbuffer 46. The analog data acquisition interface 38 connects the outputof the means for detecting AC signals 30 of the current transducer 26 tothe DSP 36 and provides for conversion of analog data from the currenttransducer 26 to a digital equivalent useable by the DSP 36. The DSP 36,under the control of software stored in the EPROM 42, receives digitaloutput from the analog data acquisition interface 38; provides controlsignals to the self test circuit 40 for testing the operation of thecurrent transducer 26, in a manner to be described in greater detailhereinafter; receives digital input from the propulsion systems 14A and14B and other vehicle subsystems through input buffer 44; and providesdigital output to the propulsion systems 14A and 14B, the HSCB 34 andother vehicle subsystems through the output buffer 46.

In accordance with the present invention, current transducer 26 includesa test winding 48, shown in phantom in FIG. 2, connected to the selftest circuit 40. In a test mode of operation, the DSP 36 causes the selftest circuit 40 to energize the test winding 48 sufficiently to causethe means for detecting AC signals 30 of the current transducer 26 toexperience AC noise of sufficient extent to cause the DSP 36 to detectscaled signals having, for example, an amplitude in excess of the secondamplitude for a duration in excess of the first interval of time, i.e.,a condition 2 signal event. If, in response to energization of the testwinding, signals having sufficient amplitude for a sufficient durationare not detected, the EMI processor 28 outputs a condition 2 signal tothe propulsion systems 14A and 14B and outputs the EMI detector faultsignal to EMI Detector Annunciator 32. In response to receiving thecondition 2 signal, the propulsion systems 14A and 14B are renderedinoperative until reset as described above. If, however, the DSP 36detects scaled signals corresponding to a condition 2 signal event, theEMI detector 24 is determined to be operational and a condition 0 signalis output to the propulsion systems 14A and 14B. In this manner, theoperation of the EMI detector 24 can be verified.

The present invention has been described above in conjunction with thedetection of AC signals at a predetermined frequency. It is to beappreciated, however, that two or more predetermined frequencies couldbe detected. Moreover, AC signals operating over one or more frequencyspectrums could also be detected using appropriate digital filteringtechniques, such as FFT. Accordingly, the use above of a predeterminedfrequency to describe the operation of the present invention is not tobe construed as limiting the invention. Furthermore, the individualfrequencies or band of frequencies comprising the AC noise to bedetected by the EMI detector could reside anywhere in a frequencyspectrum wherein such AC noise is conductible onto the DC current. Inthis respect, the EMI detector of the present invention is configurableto detect, without limitation, AC noise at one or more predeterminedfrequencies and/or AC noise over one or more continuous frequency bandsor ranges at the same time. In the present invention, the frequencies orfrequency bands to be monitored are adjustable by changing an EPROM, orby downloading new parameters or software into a RAM within the DSP.

The above invention has been described with reference to currentlypreferred embodiments. Other modifications and alterations can be madeand yet still come within the scope of the present invention. Forexample, certain characteristics of the EMI detector 24, such as,without limitation, frequency, amplitude, duration, response time,recovery criteria, and the like, are adjustable by componentsubstitution and/or software changes. The EMI detector 24 could behardware and/or software modified to detect broadband AC signals and torespond thereto in the manner set forth above. The output power of thepropulsion systems 14A and 14B could be independently adjusted to reduceEMI on the supply line 12. The EMI processor 28 could determine whetherone of the propulsion systems 14A and 14B was a primary cause of EMI andselectively adjust the output power on that propulsion system to reducethe total EMI on the supply line 12 within acceptable levels, yet makeno adjustment to the operation of the other propulsion system. It isintended that the invention be construed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

What is claimed is:
 1. A method of electromagnetic interferencedetection and control in an electrically powered vehicle, said methodcomprising the steps of:converting direct current (DC) electrical powersupplied to the vehicle to a power output at a first level; providingthe power output to an electric motor in the vehicle; monitoring the DCelectrical power for an alternating current (AC) signal appearingthereon; determining at least one of an amplitude and duration of the ACsignal; and adjusting the power output as a function of the at least oneof the amplitude and duration of the AC signal.
 2. The method as setforth in claim 1 wherein said adjusting step includes the stepsof:maintaining the power output to the electric motor at the first levelin response to the AC signal being less than a first amplitude for afirst interval of time; reducing the power output to the electric motorfrom the first level to a second level in response to the AC signalbeing greater than the first amplitude for the first interval of time;and withholding the power output from the electric motor in response tothe AC signal being greater than a second amplitude for the firstinterval of time, wherein the second amplitude is greater than the firstamplitude.
 3. The method as set forth in claim 2 wherein the maintainingstep includes maintaining the output power to the motor at the firstlevel in response to the AC signal being greater than the firstamplitude but for less than the first interval of time.
 4. The method asset forth in claim 2 wherein said adjusting step includes the stepof:isolating the vehicle from the supply of DC electrical power inresponse to the AC signal being greater than the second amplitude for asecond interval of time, wherein the second interval is greater than thefirst interval.
 5. The method as set forth in claim 4 wherein saidisolating step stops the operation of one of the converting step and theproviding step.
 6. The method as set forth in claim 1 wherein thefrequency of the AC signal monitored matches a frequency of a controlsignal for track signaling equipment used in connection with saidvehicle.
 7. The method as set forth in claim 1 wherein the frequency ofthe AC signal monitored is at least one of 60 Hz, 100 Hz and a frequencywithin the audio spectrum.
 8. A method as set forth in claim 1 furthercomprising the steps of:stimulating a current transducer with analternating current; detecting an output signal of the transducer inresponse to the stimulation; determining at least one of a frequency,amplitude and duration of the output signal; and providing power outputto the electric motor as a function of the at least one of thefrequency, amplitude and duration of the output signal.
 9. The method asset forth in claim 8 wherein the power output is provided to theelectric motor if the amplitude and duration of the output signal at aselected frequency is greater than a reference amplitude and duration atthe selected frequency.
 10. An apparatus for electromagnetic detectionand control in an electrically powered vehicle, said apparatuscomprising:means for converting direct current (DC) electrical powersupplied to the vehicle to a power output at a first level; means forproviding the power output to an electric motor in the vehicle; meansfor monitoring the DC electrical power for an alternating current (AC)signal appearing thereon; means for determining at least one of anamplitude and duration of the AC signal; and means for adjusting thepower output as a function of the at least one of the amplitude andduration of the AC signal.
 11. The apparatus as set forth in claim 10further including:means for maintaining the power output to the electricmotor at the first level in response to the AC signal being less than afirst amplitude for a first interval of time; means for reducing thepower output to the electric motor from the first level to a secondlevel in response to the AC signal being greater than the firstamplitude for the first interval of time; and means for withholding thepower output from the electric motor in response to the AC signal beinggreater than a second amplitude for the first interval of time, whereinthe second amplitude is greater than the first amplitude.
 12. Theapparatus as set forth in claim 11 wherein the maintaining meansmaintains the output power to the motor at the first level in responseto the AC signal being greater than the first amplitude but for lessthan the first interval of time.
 13. The apparatus as set forth in claim12 further including means for isolating the vehicle from the supplyline in response to the AC signal being greater than the secondamplitude for a second interval of time, wherein the second interval isgreater than the first interval.
 14. The apparatus as set forth in claim13 wherein the isolating means isolates one of the converting means andthe providing means from the supply of DC electrical power.
 15. Theapparatus as set forth in claim 10 further including:means forstimulating a current transducer with an alternating current; means fordetecting an output signal of the transducer in response to saidstimulation; means for determining at least one of a frequency,amplitude and duration of the output signal; and means for enabling theproviding means to provide power output to the electric motor as afunction of the at least one of the frequency, amplitude and duration ofthe output signal.
 16. The apparatus as set forth in claim 10, furtherincluding:means for determining a value of filter capacitance of aninput filter of the means for converting; and means for selectivelyadjusting the power output as a function of the value of the filtercapacitance.
 17. The apparatus as set forth in claim 10, furtherincluding:means for verifying the integrity of a fuse associated withone or more capacitors of an input filter of the means for converting;and means for selectively adjusting the power output as a function ofthe integrity of the fuse.
 18. An electromagnetic interference detectionand control apparatus for use with a mass transit vehicle having anelectric motor for providing motive force to the vehicle and apropulsion system for converting electrical power supplied to thevehicle via a supply line to an electrical power useable by the motor,wherein the propulsion system supplies the converted electrical power tothe motor at a first level, said apparatus comprising:a currenttransducer for detecting AC current on the supply line and for providingan output signal related thereto; and an EMI processor receiving theoutput signal of the current transducer and connected to the propulsionsystem for analyzing the detected AC current over a first interval oftime and for causing the electrical power supplied to the motor by thepropulsion system to be adjusted as a function thereof.
 19. Theapparatus as set forth in claim 18 wherein the EMI processor signals thepropulsion system to maintain the electrical power supplied to the motorby the propulsion system at the first level in response to the detectedAC current being less than a first amplitude.
 20. The apparatus as setforth in claim 18 wherein the EMI processor reduces the electrical powersupplied to the motor by the propulsion system from the first level to asecond level in response to the detected AC current exceeding a firstamplitude for said first interval of time.
 21. The apparatus as setforth in claim 20 wherein the EMI processor restores electrical power tothe motor to the first level in response to the AC current falling belowthe first amplitude for a predetermined interval of time.
 22. Theapparatus as set forth in claim 18 wherein the EMI processor generates asignal that causes the propulsion system to cease providing electricalpower to the motor when the detected AC current exceeds a secondamplitude for said first interval of time, with said second amplitudebeing greater than the first amplitude.
 23. The apparatus as set forthin claim 22 wherein the vehicle further includes a circuit breakerdisposed between the supply line and the propulsion system, the EMIprocessor causing the circuit breaker to open and isolate the propulsionsystem from the supply line in the absence of the propulsion systemacknowledging the EMI processor signal to cease providing electricalpower to the motor.
 24. The apparatus as set forth in claim 23 whereinthe EMI processor causes the circuit breaker to open and isolate thepropulsion system from the supply line in response to the detected ACcurrent exceeding the second amplitude for a second interval of time,with the second interval being greater than said first interval.
 25. Theapparatus as set forth in claim 18 further including means forstimulating said transducer to detect current exceeding a predeterminedamplitude for a predetermined interval of time.
 26. The apparatus as setforth in claim 18 wherein the EMI processor monitors the output of thecurrent transducer at a frequency corresponding to a control signalfrequency for track signaling equipment utilized in conjunction with thevehicle.
 27. An electrically propelled vehicle comprising:an electricmotor for imparting motive force to the vehicle; a propulsion system forconverting DC electrical power supplied to the vehicle via a supply lineto an electrical output useable by the motor, with the electrical outputprovided at a first level; and an EMI detector including:a currenttransducer for detecting noise on the supply line and for providing anoutput related thereto; and a controller connected to the transducer andto the propulsion system for determining when the output of thetransducer exceeds a first amplitude for a first interval of time andfor signaling the propulsion system to reduce the electrical output fromthe first level to a second level in response thereto.
 28. The vehicleas set forth in claim 27 wherein the controller monitors the output ofthe transducer at one or more of a predetermined frequency and a band offrequencies.
 29. The vehicle as set forth in claim 27 wherein the secondlevel is 50% of the first level.
 30. The vehicle as set forth in claim27 wherein the controller causes the propulsion system to reduce poweroutput to 0% in response to the transducer output being in excess of asecond amplitude for the first period of time, with the second amplitudegreater than said first amplitude.
 31. The vehicle as set forth in claim30 further including a circuit breaker disposed between the supply lineand the propulsion system and connected to the controller, with thecontroller causing the circuit breaker to open and isolate thepropulsion system from the supply of DC electrical power in response tothe output of the transducer being in excess of the second amplitude fora second interval of time, with the second interval being greater thansaid first interval.
 32. The vehicle as set forth in claim 30 whereinthe propulsion system signals the controller when output power isreduced to 0%.
 33. The vehicle as set forth in claim 32 wherein thecontroller signals a circuit breaker to open thereby isolating thepropulsion system from the supply line in the absence of receiving thesignal from the propulsion system when output power is reduced to 0%.